The invention relates to novel superalloy compositions having limited density and exhibiting, when hot, good mechanical properties as well as good resistance to oxidation and corrosion. The invention relates in particular to the application of such superalloys to form parts of a turbomachine.

aeronautics.

Prior art

Within the framework of the development of new generation aeronautical turbines, it is sought for materials having a resistance to oxidation and to hot corrosion (typically in the range 800 ° C-1000 ° C) as well as an improved density. limited.

With this in mind, so-called high entropy alloys (“High Entropy Alloy”;

“HEA”) or complex concentrated alloys (“Complex Concentrated Alloys”) have been developed. In particular, work has been carried out to identify new alloys exhibiting precipitates of gamma-prime hardening phases in the alloy matrix.

However, it has been observed that, during exposure to high temperature, the microstructure of these alloys can be affected insofar as there may be appearance of particles of undesirable phases, namely topologically compact phases that weaken ("Topologically Close -Packed ";" TCP "). The appearance of these phases can lead to a lowering of the mechanical properties of the alloy.

JP 2018-145456 is known which discloses high entropy alloys.

It is therefore desirable to have new alloy compositions having a limited density and exhibiting, when hot, good mechanical properties as well as good resistance to oxidation and to corrosion.

Disclosure of the invention

To this end, the invention proposes, according to a first embodiment, a

nickel-based superalloy comprising, in atomic percentages, 13% to 21% chromium, 4% to 30% cobalt, 4% to 10% aluminum, 4.5% to 10% titanium, 8% to 18 % iron, optionally boron in an atomic percentage less than or equal to 0.5%, optionally carbon in an atomic percentage less than or equal to 1%, optionally at least one additional element chosen from molybdenum, tungsten, tantalum and niobium, the total atomic content of the additional element (s) being less than or equal to 1.5%, the remainder being constituted by nickel and inevitable impurities, with the sum of

atomic percentages of aluminum and titanium between 8.5% and 15%.

The invention further proposes, according to a second embodiment, a

cobalt-based superalloy comprising, in atomic percentages, 9% to 20% chromium, 22% to 36% nickel, 4% to 10% aluminum, 4% to 10% titanium, 8% to 18% iron, optionally boron in an atomic percentage less than or equal to 0.5%, optionally carbon in an atomic percentage less than or equal to 1%, optionally at least one additional element chosen from molybdenum, tungsten, tantalum and niobium, the total atomic content of the additional element (s) being less than or equal to 1.5%, the remainder being constituted by cobalt and inevitable impurities, with the sum of the atomic percentages of aluminum and titanium between 8% and 15%.

The term “superalloy based on X” is understood to mean a superalloy in which the element X is the major element in atomic percentage. Element X is therefore the element with the highest atomic percentage in the superalloy. The atomic percentage of the element X in the X-based superalloy can, but need not be, greater than 50%.

"Unavoidable impurities" are elements which are not intentionally added to the composition and which are supplied with other elements.

The two embodiments described above both relate to

high entropy superalloys, with a complex composition having a matrix, called the gamma phase, in which precipitates of hardening phases of the gamma-prime (L1 2 ) type are present in a significant volume fraction to optimize the mechanical properties at high temperature. The volume fractions of the precipitates L1 2 (denoted "X (L1 2 )") preferably satisfy the following conditions:

- 50% ³ X (L1 2 ) ³ 40% at 800 ° C, and

- 30% ³ X (L1 2 ) ³ 20% at 1000 ° C.

In addition, the superalloys according to the two embodiments described above advantageously have a low propensity to form phases.

topologically compact weakening. In these superalloys, the incorporation of elements chosen from molybdenum, tungsten, tantalum and niobium is minimized (sum of the contents of these four elements less than or equal to 1.5% in atomic percentages) in order to give them a reduced density. The controlled presence of these elements is noted however that may be advantageous in order to further harden the matrix and the phases Ll 2 . The superalloys described above also exhibit good resistance to oxidation and to hot corrosion.

The advantageous properties of the superalloys described above will be repeated throughout the description which follows indicating the contribution of each of the alloying elements.

Chromium gives the superalloy good resistance to oxidation and corrosion at high temperature, typically in the temperature range between 800 ° C and 1000 ° C. If the chromium content is too high, this tends to reduce the solvus temperature of the gamma-prime phases, that is to say the temperature above which these phases are dissolved in the gamma matrix. Beyond the solvus temperature, the gamma-prime phases are dissolved and no longer participate in the increase in hardness of the superalloy. Chromium must therefore be present in an amount sufficient to provide the desired resistance to oxidation and corrosion, but its amount must also be limited in order to retain the precipitates of the gamma-prime phases, and therefore the increase in hardness of the superalloy, over a wide temperature range. Limiting the chromium content in the

The superalloy also has the advantage of reducing the formation of topologically compact phases which weaken with iron, such as the sigma phase or the B2 phase.

In the case of the first embodiment relating to the nickel-based superalloy, the cobalt makes it possible to reinforce the gamma matrix and to reduce the sensitivity to the precipitation of topologically compact weakening phases. The cobalt also makes it possible to slow down the diffusion of the species, thus promoting the stability of the gamma-prime precipitates. As for chromium, the cobalt content must however be limited so that the solvus temperature of the gamma-prime phases remains high.

In the case of the second embodiment relating to the cobalt-based superalloy, the nickel makes it possible to extend the domain of existence of the gamma-prime phase and the solvus of this phase. The nickel content must however be limited in order to retain gamma-prime phases doped with cobalt and not to form the T-Ti (Ni, Co) 3 phase at operating temperature.

Aluminum and titanium promote the precipitation of gamma-prime hardening phases which have a composition between (Ni, Co) 3 (Al, Ti) and C0 3 T1. However, the addition of aluminum and titanium must be carried out in limited proportions so that the gamma matrix always occupies a significant fraction of the superalloy and thus prevent the mechanical properties at low temperature from being adversely affected.

Iron makes it possible to decrease the density of the superalloy insofar as this element has a lower density than that of nickel or cobalt. That is

particularly advantageous when the superalloy is intended for use in the aeronautical field where the fact of being able to lighten the mass of the parts is of particular interest. However, it is necessary to limit the proportion of iron so as not to promote the formation of iron oxides to the detriment of chromium oxides, and thus to maintain the desired resistance to oxidation and to hot corrosion.

Other elements may be present in the superalloy as an option and in a limited quantity, namely boron or carbon if the formation of borides or carbides is sought in order to reinforce the strength of the grain boundaries. The inevitable impurities can, for their part, be present in an atomic percentage less than or equal to 1000 ppm.

The part which will follow attempts to describe the preferential characteristics of the compositions of the superalloys.

In the case of the second embodiment, the superalloy can comprise between 13% and 21% chromium in atomic percentages.

Such a chromium content makes it possible to further increase the resistance to oxidation and to hot corrosion.

In an exemplary embodiment, the superalloy comprises between 4% and 8%, for example between 4.5% and 8%, of aluminum in atomic percentages. the

superalloy can comprise between 4.5% and 7.5%, for example between 4.5% and 5.5%, aluminum in atomic percentages.

Such aluminum contents participate in optimizing, as a whole, the mechanical properties exhibited by the hot alloy.

In an exemplary embodiment, the superalloy comprises between 4.5% and 8%, of titanium in atomic percentages.

Such a titanium content contributes to optimizing, as a whole, the mechanical properties exhibited by the hot alloy.

In an exemplary embodiment, the sum of the atomic percentages of aluminum and titanium is between 9% and 13%.

Such a content contributes to optimizing, as a whole, the properties

mechanical features of the hot alloy.

In the case of the first embodiment, the superalloy can comprise between 15% and 26% of cobalt in atomic percentages. In particular, the superalloy can comprise between 15% and 22% of cobalt in atomic percentages.

Such cobalt contents make it possible to optimize the compromise between stability of the gamma-prime hardening phases and reinforcement of the gamma matrix provided by the cobalt.

In the case of the first embodiment, the superalloy can comprise between 9% and 18% iron in atomic percentages. In particular, the superalloy may comprise between 13% and 18% iron in atomic percentages, for example between 14% and 18% iron in atomic percentages, or even between 15% and 18% iron in atomic percentages.

Such iron contents make it possible to optimize the compromise between reduction in the mass of the superalloy and resistance to oxidation and to hot corrosion.

In the case of the first embodiment, the sum of the atomic percentages of chromium and iron may be less than or equal to 35%, for example between 20% and 34%.

In the case of the first embodiment, the difference between the atomic percentage of nickel and the atomic percentage of cobalt (Ni-Co) can be between 5% and 50%, for example between 10% and 48%.

In the case of the first embodiment, the superalloy may comprise, in atomic percentages, 13% to 21% chromium, 4% to 30% cobalt, 4% to 8% aluminum, 4.5% to 8% titanium and 8% to 18% iron.

In the case of the first embodiment, the superalloy may comprise, in atomic percentages, 13% to 17% chromium, 16% to 23% cobalt, 4% to 8% aluminum, 4.5% to 8% titanium and 15% to 18% iron.

In the case of the first embodiment, the superalloy may comprise, in atomic percentages, 16% to 17% chromium, 16% to 17% cobalt, 4.5% to 5.5% aluminum, 4.5 % to 5.5% titanium and 16% to 17% iron.

In the case of the first embodiment, the superalloy may comprise, in atomic percentages, 13% to 14% chromium, 21.5% to 22.5% cobalt, 4.5% to 5.5% aluminum. , 7% to 8% titanium and 17% to 18% iron.

In the case of the first embodiment, the superalloy may comprise, in atomic percentages, 13% to 21% chromium, 24% to 26% cobalt, 4% to 8% aluminum, 4.5% to 8% titanium and 8% to 11% iron.

In the case of the first embodiment, the superalloy may comprise, in atomic percentages, 19.5% to 20.5% chromium, 24.5% to 25.5% cobalt, 4.5% to 5.5 % aluminum, 4.5% to 5.5% titanium and 9.5% to 10.5% iron.

In the case of the first embodiment, the superalloy may comprise, in atomic percentages, 13% to 14% chromium, 24.5% to 25.5% cobalt, 5% to 6% aluminum, 6.5 % to 7.5% titanium and 8.5% to 9.5% iron.

In the case of the second embodiment, the superalloy can comprise between 25% and 36% of nickel in atomic percentages.

In the case of the second embodiment, the superalloy can comprise between 8% and 15% iron in atomic percentages.

Such an iron content makes it possible to optimize the compromise between reduction in the mass of the superalloy and resistance to oxidation and to hot corrosion.

In the case of the second embodiment, the sum of the atomic percentages of chromium and iron may be between 18% and 35%, for example between 19% and 24%.

In the case of the second embodiment, the difference between the atomic percentage of cobalt and the atomic percentage of nickel (Co-Ni) may be less than or equal to 10%.

The invention also relates to a turbomachine part comprising a superalloy as described above. The turbomachine part may be a part of

aeronautical turbomachine. The turbomachine part can be chosen from: a turbomachine disc, a turbomachine casing, a movable vane, a fixed vane, part of a combustion chamber, part of a post-combustion chamber, a ring sector turbine, a thrust reverser or a fastener such as a bolt.

The invention also relates to a turbomachine comprising a turbomachine part as described above. The turbomachine can be a

turbomachine aéronautique.

On vient de décrire la structure et des applications possibles pour le superalliage selon l'invention. Le passage ci-dessous s'attache à décrire des détails de fabrication du superalliage selon l'invention.

Dans un premier temps, le superalliage de composition décrit plus haut est obtenu par un procédé classique comme la refusion à l'arc sous vide (« Vacuum Arc Remelting » ; « VAR ») ou la fusion sous vide par induction (« Vacuum Induction Melting » ; « VIM »). On peut encore obtenir une pièce du superalliage par forgeage, extrusion ou laminage. La pièce peut encore être obtenue à partir d'une poudre elle-même formée par pulvérisation d'un lingot du superalliage.

Dans un deuxième temps, la pièce brute de solidification ou de mise en forme est traitée thermiquement.

On peut ainsi réaliser un traitement thermique de la microstructure permettant de dissoudre les précipités de phases gamma-prime, d'éliminer les ségrégations ou, à défaut, de les réduire significativement. Ce traitement est réalisé à une température supérieure à la température de solvus des phases gamma-prime et inférieure à la température de fusion commençante du superalliage (Tsolidus). Ce traitement peut être réalisé à une température supérieure ou égale à 1100°C, par exemple comprise entre 1100°C et 1200°C.

Une trempe peut ensuite être réalisée après le traitement thermique afin d'obtenir une dispersion fine et homogène des précipités de phases gamma-prime. Le superalliage peut être refroidi jusqu'à une température de fin de trempe inférieure ou égale à 850°C, par exemple comprise entre 20°C et 850°C, durant le traitement de trempe.

Un traitement thermique de revenu peut ensuite être réalisé après la trempe à une température inférieure à la température de solvus des phases gamma-prime afin de figer la microstructure du superalliage. Le traitement thermique de revenu peut être réalisé à une température comprise entre 750°C et 1000°C. On obtient ainsi une

microstructure stable dans laquelle les précipités de phases gamma-prime sont présents en une fraction significative.

On peut ensuite usiner la pièce obtenue afin d'ajuster ses dimensions.

Brève description des dessins

[Fig. 1] La figure 1 est un ensemble de photographies qui montrent la microstructure de plusieurs exemples de superalliages selon l'invention.

[Fig. 2] FIG. 2 is a test result quantifying the volume fractions occupied by the hot gamma-prime precipitates for several examples of superalloys according to the invention.

[Fig. 3] FIG. 3 is a test result quantifying the mean radius of the hot gamma-prime precipitates for several examples of superalloys according to the invention.

[Fig. 4] FIG. 4 is a test result quantifying the experimental densities of several examples of superalloys according to the invention.

[Fig. 5] FIG. 5 is a result of analysis by differential scanning calorimetry (“Differential Scanning Calorimetry”; “DSC”) carried out on several examples of superalloys according to the invention.

[Fig. 6] FIG. 6 is a test result comparing the compressibility of several examples of superalloys according to the invention with that of commercial superalloys outside the invention.

[Fig. 7] FIG. 7 shows the evolution of the hardness of an example of a superalloy according to the invention during annealing at 900 ° C.

Description of the embodiments

The inventors have evaluated the performance of several examples of superalloys according to the invention. The various tests which were carried out will be detailed below.

The compositions evaluated are detailed in Table 1 below. The contents of the various elements are indicated in atomic percentages.

[Table 1]

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The TA1-TA5 alloys were subjected to a heat treatment in which a first level was imposed at 1150 ° C. for 48 hours followed by a second level at 900 ° C. for 403 hours. Figure 1 shows the microstructure of the TA1-TA5 alloys evaluated. The photographs of FIG. 1 show the presence of precipitates of gamma-prime phases in each of the TA1-TA5 alloys.

The TA1-TA5 alloys were subjected to a heat treatment at 900 ° C for a period of 403 hours. The volume fraction of the gamma-prime phase precipitates was evaluated using the following method: automated thresholding of 20 images taken by scanning electron microscopy at a magnification of x5000. FIG. 2 quantifies the volume fractions occupied by the gamma-prime precipitates for the TA1-TA5 alloys. It is observed that the precipitates of gamma-prime phases occupy a significant volume fraction thus providing the desired hot hardening.

The mean radius of the precipitates was also evaluated by the following method: thresholding of SEM images to obtain about 1500 precipitates per composition, the mean radius is defined as being the radius of a disk of equivalent surface. The results are provided in FIG. 3. It is observed that gamma-prime precipitates of relatively small size, and therefore relatively stable, have been obtained. Whatever the embodiment considered, the mean radius of the gamma-prime precipitates can be

less than or equal to 200 nm. It will be noted that this size of the precipitates remains stable even after exposure to high temperatures. It has, moreover, been verified by measurements of oxidation kinetic constants that the superalloys according to the invention are classified in the field of chrominformers by protecting themselves by forming protective layers of chromium oxide Cr 2 03.

The experimental densities of the TA1-TA5 alloys were quantified and the results obtained are provided in FIG. 4. It is noted that the superalloys according to the invention have limited densities, all of them less than 8.1 g / cm 3 .

The window of dissolution of the TA1-TA5 alloys was evaluated by means of a differential scanning calorimetry analysis (see FIG. 5). It is found that the solvus temperature of each of the alloys is relatively high and close to 1100 ° C, thus indicating the effective contribution of these precipitates to the increase in hot hardness over a wide temperature range.

The compressibility of the alloys was evaluated at 900 ° C. on a Gleeble machine and compared with that of the commercial alloy Inconel 718 outside the invention (see FIG. 6). The superalloys according to the invention have good mechanical properties, superior to those of the Inconel 718 alloy, while having a density

significantly lower.

FIG. 7 illustrates, for its part, the evolution of the hardness, measured at 25 ° C, of ​​the TA5 alloy during annealing at 900 ° C. The hardness of the alloy remains above 430 Hv even after several hours at high temperature.

Other examples of alloy compositions than those indicated in Table 1 above have been identified as preferential by the inventors, to

know (compositions given in atomic percentages):

- TA6: 40.4% Ni-25.2% Co-13, l% Cr-8.8% Fe-5.5% AI-7% Ti, and

- TA7: 28% Ni-37.6% Co-13.1% Cr-8.8% Fe-4.5% Al-8% Ti.

The expression "included between ... and ..." should be understood as including the limits.

WE CLAIMS

[Claim 1] Nickel-based superalloy comprising, in atomic percentages, 13% to 21% chromium, 15% to 26% cobalt, 4% to 10% aluminum, 4.5% to 10% titanium, 8% to 18% iron, possibly boron in one

atomic percentage less than or equal to 0.5%, optionally carbon in an atomic percentage less than or equal to 1%, optionally at least one additional element chosen from molybdenum, tungsten, tantalum and niobium, the total atomic content of or additional element (s) being less than or equal to 1.5%, the remainder consisting of nickel and inevitable impurities, with the sum of the atomic percentages of aluminum and titanium between 8.5% and 15%.

[Claim 2] Cobalt-based superalloy comprising, in atomic percentages, 9% to 20% chromium, 22% to 36% nickel, 4% to 10% aluminum, 4% to 10% titanium, 8% with 15% iron, optionally boron in an atomic percentage less than or equal to 0.5%, optionally carbon in an atomic percentage less than or equal to 1%, optionally at least one additional element chosen from molybdenum, tungsten, tantalum and niobium, the total atomic content of the additional element (s) being less than or equal to 1.5%, the remainder being constituted by cobalt and inevitable impurities, with the sum of the atomic percentages of 'aluminum and titanium between 8% and 15%.

[Claim 3] A superalloy according to claim 1 or 2 comprising between 4.5% and 7.5% aluminum in atomic percentages.

[Claim 4] A superalloy according to claim 1 or claim 3 appended to claim 1 comprising between 15% and 22% cobalt in atomic percentages.

[Claim 5] A superalloy according to claim 1 or any one of claims 3 or 4 appended to claim 1 comprising between 13% and 18% iron in atomic percentages.

[Claim 6] A superalloy according to claim 1 comprising, in atomic percentages, 13% to 21% chromium, 15% to 26% cobalt, 4% to 8% aluminum, 4.5% to 8% titanium and 8% to 18% iron.

[Claim 7] A superalloy according to claim 6 comprising, in atomic percentages, 13% to 17% chromium, 16% to 23% cobalt, 4% to 8% aluminum, 4.5% to 8% titanium and 15% to 18% iron.

[Claim 8] A superalloy according to claim 7 comprising, in atomic percentages, 16% to 17% chromium, 16% to 17% cobalt, 4.5% to 5.5% aluminum, 4.5% to 5.5% titanium and 16% to 17% iron.

[Claim 9] A superalloy according to claim 7 comprising, in atomic percentages, 13% to 14% chromium, 21.5% to 22.5% cobalt, 4.5% to 5.5% aluminum, 7 % to 8% titanium and 17% to 18% iron.

[Claim 10] A superalloy according to claim 6 comprising, in atomic percentages, 13% to 21% chromium, 24% to 26% cobalt, 4% to 8% aluminum, 4.5% to 8% titanium and 8% to 11% iron.

[Claim 11] A superalloy according to claim 10 comprising, in atomic percentages, 19.5% to 20.5% chromium, 24.5% to 25.5% cobalt, 4.5% to 5.5% d aluminum, 4.5% to 5.5% titanium and 9.5% to 10.5% iron.

[Claim 12] A superalloy according to claim 10 comprising, in atomic percentages, 13% to 14% chromium, 24.5% to 25.5% cobalt, 5% to 6% aluminum, 6.5% to 7.5% titanium and 8.5% to 9.5% iron.

[Claim 13] A superalloy according to claim 2 or claim 3 appended to claim 2 comprising between 25% and 36% nickel in atomic percentages.

[Claim 14] A turbomachine part comprising a superalloy according to any one of claims 1 to 13.

[Claim 15] A turbomachine comprising a turbomachine part according to claim 14.